Pilots of fatal Asiana Airlines crash knew speed was low

A burned Boeing Co. 777, operated by Asiana Airlines Inc., sits on the runway after it crashed landed at San Francisco International Airport (SFO) in San Francisco, California on July 6, 2013.

Pilots of an Asiana Airlines plane that crash-landed in San Francisco in July were aware that the plane was traveling too slowly and tried to correct it in the final seconds before impact, documents released on Wednesday by U.S. aviation safety investigators show.

The crash on July 6 killed three people and injured more than 180, the first fatal commercial airplane crash in the U.S. since February 2009. The co-pilot of the jet, who was training the pilot flying the plane, thought the auto-throttle on the Boeing 777 plane might not have been operating, the documents show.

The pilot who was flying the plane said he wasn't sure whether auto-throttle was maintaining speed, documents show.

The low, slow landing caused the plane's tail to hit a seawall short of the runway. The plane spun 330 degrees as it broke apart and caught fire, strewing wreckage along the runway.

The National Transportation Safety Board released dozens of detailed documents related to the crash as it opened an investigative hearing into its causes.